ceramicafandomcom-20200216-history
On staining glass
Categoría:Libros Category:Collections of essays Category:Art Categoría:Libros EN Categoría:Arte Categoría:Libro arte Category:Franklin Institute On Staining Glass. By Professor Schubarth. Mode of Obtaining a Red Color by means of Oxide of Copper left The ancients were acquainted with the means of staining glass by the employment of oxide of copper; it is mentioned by Neri and Kunckel, in their works. The art was however so completely lost at the close of the last century, that it was generally believed that glass was always stained red by means of Cassius purple. It was not until 1828 that M. Engelhardt, of Zinsweiler, succeeded in staining glass red by means of a mixture of equal parts of oxide of copper and protoxide of tin : this process was tried with success in the glass manufactory at Hoffurmgsthal, Silesia. The protoxide of tin is now done away with, and the compound employed is nearly the same as that mentioned by Neri, but more simple. It is composed of a mixture of copper scales (which are almost entirely composed of oxide), and oxide of tin (zinnasche) obtained by the oxidation of that metal in a state of fusion in contact with the air, to which a small quantity of iron filings is sometimes added, when a scarlet tint is required to be produced. Should the color by accident disappear, it may be brought out by again bringing the copper into the state of oxide ; this is done by introducing into the vessel a small quantity of tin or iron scale. It will of course be understood that the glass to be operated upon must not contain saltpetre, nor any other oxidizing substance. Glass stained by means of oxide of copper is of a very deep color, and can only be worked in thin sheets, and by covering it with a thick colorless glass (plate glass.) Obtaining a Red Color by means of Gold The employment of gold for staining glass red does not appear to have been known to the ancients, and the period when it was first used, and by whom, cannot be ascertained. In the seventeenth century Kunckel employed Cassius purple for staining glass a ruby color; this was discovered by A. Cassius a short time previous; but the recipe employed by Kunckel was not generally known until it was published in 1836, by M. Metzger, proprietor of the glass-works at Zechlin, on the occasion of M. Fuss' researches. It must not be imagined from this, as some persons have lately stated, that it is necessary to use gold in the state of Cassius purple. Neri, at the end of the sixteenth and commencement of the seventeenth century, stated, that in order to stain glass a ruby color, it was only necessary to employ calcined chloride of gold. At a later period, Libar wrote to the same effect, and Merret certified that he had proved the efficacy of the process. In 1834 Golfier Besseyre stated, in the Journal of Pharmacy, that Douault Wieland colored his paste with perchloride of gold only. Lastly, in 1836, Fuss writes, that in Bohemia all the ruby-colored glass was prepared with chloride of gold Vol. XI, 3m> Series.—No. 3.—March, 1S46. 16 only, and that glass might be stained red as well with metallic gold, as with oxide of gold or Cassius purple. It is therefore a fact known for some time, that glass may be stained red, without either Cassius purple or oxide of tin, with metallic gold or preparations of gold. In the glass-works of Bohemia and Silesia perchloride of gold only is used, without the addition of oxide of tin, in order to produce their fine rose or carmine-colored glass. If powdered gold be triturated with twenty times its weight of enamel fritt, a light red or pink mass will be produced, without any metallic lustre. By healing for a length of time at a temperature of 110° of Wedgwood's pyrometer, a compound of metallic gold and quartz ground very fine upon porphyry, and intimately mixed, the latter will be stained a pink color. Pieces of gilt porcelain which have been a long time in use, are stained red at those parts where nearly the whole of the gold had become worn off; gold volatilizes under the action of a powerful electric battery, or the heat of the oxyhydrogen blow-pipe in the form of a very light purple powder. Fulminating gold, in detonating upon a silver plate also leaves thereon a purplish powder: if this latter is then mixed with silica and heated, it will be stained a reddish color; the gold exists in very minute particles, but not in the state of oxide. left If, by the aid of heat, a solution of gold in aqua regia be decomposed by means of oxalic acid, the liquor appears green and even blue, and a brownish powder is precipitated, the particles of which touching the sides of the receiver are yellow, and have metallic lustre. It is certain that this green, blue, brown, and sometimes yellow powder is metallic gold. If perchloride of gold be treated with albumen and the precipitate exposed to the action of the solar rays, it will assume a red tint. A solution of gold colors the skin red. Silk dyed with perchloride of gold becomes blue, green, and purple, under the action of the solar rays. All these effects are certainly due to metallic gold. It is evident that at the temperature of glass-houses, which is more than sufficiently high to effect the fusion of the glass, the gold contained in the Cassius purple will be brought back into the metallic state, whatever may be supposed to be the nature of this compound, upon which chemists have not yet agreed. If Cassius purple, chloride of gold, or gold leaf, be heated with borax or glass containing lead, to a temperature of 32° of Wedgwood's pyrometer, the gold will be precipitated in small globules at the bottom of the crucible, and if the heat be increased, the borax or glass will successively assume a yellow, brownish yellow, green, and bluish green, orange, deep orange, and lastly, a purple red color, according as the temperature is raised and kept up. We have verified the following fact stated by Golfier Besseyre :— On triturating gold powder chemically pure with soot, mixing it intimately with a composition of glass containing lead (commonly called flint glass), and melting the whole in a glass-furnace,a glass is produced perfectly colorless at top, and presenting successively the following colors from top to bottom, viz :—greenish-yellow, topaz-yellow, yel lowish-brown, dark reddish-brown, and is even in some parts towards the bottom rather dull. M. Pohl has observed, that flint glass mixed with a small quantity of perchloride of gold, generally appears green after melting and cooling, some parts only having a red tint. On the contrary, on melting together glass containing a very small proportion of red lead and a small quantity of borax, with a solution in aqua regia of 6 ducats to 48 lbs. of fritt, after remaining in a state of fusion for six or seven hours, a perfectly colorless glass is obtained, which when worked into very thin plates, takes, upon cooling, a fine red color. Knox states that gold melted with glass stains it green, which is deeper in proportion to the quantity of silica it contains, and that if the temperature be raised, it changes to pale red. |left It is well known that colorless glass containing no lead, but containing gold, remains colorless when cooled very slowly, but takes a red color when cooled suddenly, or when re-heated to a dull red heat. Splittgerber has lately proved that this takes place in a similar manner in atmospheric air, oxygen and hydrogen, surrounded by sand, by coal-dust, and protoxide of zinc, or in nitre and chlorate of potash melted: it cannot then be attributed to oxidation or reduction, but simply to a molecular change of the particles of gold, produced by the action of heat. Golfier Besseyre observes, that on melting glass which has been stained red by gold, and keeping it in a state of fusion for some time, and cooling it very slowly, it becomes colorless, and on being again heated, again takes a red tint, bordering upon violet. By repeating this operation, the glass successively assumes violet and blue colors, and finally becomes completely colorless. Splittgerber confirms this fact by stating, that he had observed the density of colored glass to be somewhat less than that of colorless glass. When glass stained by means of gold is heated too often, or exposed to too high a temperature, it takes a light brown color, loses its transparency, and will not again take ared color; on being looked through; it will be seen that some parts are colored a fine blue and bluish green, and grains of gold of various sizes may be seen with the naked eye (this state bears the greatest analogy to the phenomenon presented by a solution of gold slightly heated with oxalic acid.) Pieces of colorless glass containing gold, cooled very suddenly, cannot by any known means be made to take a red color, and remain perfectly colorless. In conclusion we may state 1st. That in order to stain glass a red color by means of gold, it is not necessary to use Cassius purple, or to add to the chloride of gold either oxide of tin, or oxide of antimony. 2ndly. That by the addition of chloride of gold, or even metallic gold in minute particles, either to a very fusible glass or lead, or soda glass, containing a very small portion of minium (red oxide of lead,) glass may be produced which will take a red color whilst being worked. left 3rdly. That if Cassius purple be employed, it will be decomposed during the fusion of the glass, and metallic gold will be precipitated from it. 4thly. That on grinding metallic gold to fine powder, upon porphery with hard substances, a red colored mixture will be produced. 5thly. That the coloring of the glass appears in all probability to arise from gold in a very comminuted state. Several other metallic bodies present analogous phenomena. Platinum and iridium in powder, mixed with enamel or fritt, prodnce a fine non-metallic black. Metallic silver colors glass a transparent yellow, seen by refraction, and an opaque grayish and bluish green, seen by reflection. If this glass be heated too often it becomes semi-opaque, and small grains of silver appear ; this is precisely similar to the effect produced by gold. In conclusion, it will be sufficient to cite the remarkable changes of color produced by a change in the molecular state of iodide of mercury, carbon, sulphur, solenium, phosphorus, mercury, oxide of iron, &c, to prove that there is nothing to prevent gold presenting the same phenomena. Obtaining a Blue Color by oxide of Copper It is known that oxide of copper furnishes green or blue solutions; and will also stain glass a fine emerald green and light blue, turquoise blue, and sky blue. For some years past a white milky glass has been manufactured in Bohemia and Silesia, known under the name of alabaster glass. The composition of this glass does not differ from that of ordinary crystal. (Bohemian crystal is a glass made without lead, with potash for its base.) After the glass has been melted, it is poured off and stirred up. A second charge is then melted, to which is added, when the fusion is complete, the glass previously stirred and cooled, which cools the mass; and as soon as it is melted, it is to be worked at the lowest possible temperature. The glass will be of a milky white, while if the temperature were much raised, it would become colorless and transparent. If oxide or sulphate of copper be added to a colorless glass, and the temperature is sufficiently high, a transparent glass of a bluish green tint will be obtained. If the operation has been carried on as above stated to obtain a milky glass, it will be of a turquoise-blue color. Lastly, if this turquoise-blue colored glass be re-melted, ata high temperature, a transparent aqua-marine blue will be produced.—Bulletin de la Sociele d' Encouragement. Lon. Jour, of Arts and Sci. * Journal of the Franklin Institute , Volumen 41 (Google eBook). Pergamon Press, 1846. Véase en Google Category:Glass categoría:pigmentos Categoría:Cobre Categoría:Libros Categoría:1846 Categoría:ES-O